This invention relates to an improvement of the method for horizontal ribbon crystal growth (for example, Publication of Japanese Patent Application No. 28388/78), in which thin and flat ribbon crystals of a crystalline substance, such as semi-conductor silicon or the like, is drawn out in a horizontal direction, while crystallizing at the growing tip of a seed crystal, from the horizontal free surface of a melt of said crystalline substance. In particular, this invention provides means for preventing an irregular shape of the grown ribbon crystal, which often occurred in the prior art method and became the cause of an interruption of operation.
In the following the, usual method for horizontal ribbon crystal growth will be explained with reference to FIG. 1.
FIG.1 is a vertical cross sectional view of a melt containing crucible showing when a ribbon crystal is drawn out. The upper surface 1a of melt 1 of high purity silicon is raised up beyond the level of upper edge 2c of a high purity quartz crucible 2. The melt 1 is heated by a heater 6 arranged so as to surround the circumference of a peripheral wall 5a and the whole area of bottom portion 5b of a heat refractory crucible 5 which holds said crucible 2. Plate 7 is a shielding against heat. After contacting the seed crystal 3 with the upper surface 1a of said melt 1 cooling gas from a cooler 4 is blown upon the contact interface (solid-liquid interface) 3a between the seed crystal 3 and the melt 1, thereby the solid-liquid interface 3a is undercooled to cause crystal (sprout crystal) growth on this interface 3a. After the sprout crystal begins to grow, the seed crystal 3 is drawn out in a horizontal direction with a velocity equal to the velocity of crystal growth and, thereby ribbon crystal is grown.
In the above described method, since the bottom portion 5b of the crucible 5 is uniformly heated over the whole area thereof to the same degree as the peripheral wall 5a, the state of the melt is such that on the lower side of the solid-liquid interface 3a, there exists a heat conducting layer having a downward temperature gradient. Consequently, since the undercooling spreads from the solid-liquid interface 3a in the downward direction in a short time, there often occurs a down-growth 3d (usually, 5-10 mm) at the junction 3c between the seed crystal 3 and grown crystal 3b at the beginning of sprout crystal growth, as shown in FIG. 2(a), and when the junction 3c is drawn out of the crucible 2, as shown in FIG. 2(b), due to the existence of a recess 3e adjacent to said large down-growth 3d, it occurs that attracted melt 1 escapes out of the crucible 2 accompained with said drawing and is impossible to return into the crucible 2 and, spills down and due to the siphon effect of this spilling a large amount of melt 1 will be lost so that the upper surface 1a of the melt 1 will go down to a lower level than the upper edge 2c of the crucible 2. Further, at the time of said spilling of the melt 1, the upper surface 1a will be disturbed so that the grown crystal 3b separates from the upper surface 1a causing polycrystal growth having irregular shape.